In general, in a fuel pipeline system of an automobile, there is employed such a mechanism that, when an engine is operated, a fuel such as gasoline or an alcohol-added gasoline (gasohol) is sucked from an inside of a fuel tank to be supplied whenever necessary. At this time, the suction of the fuel is carried out with a pump permanently installed in the fuel tank (referred to as “fuel pump”). Further, a hose coupled to the fuel pump in the a fuel tank is called an in-tank tube, and the hose is also permanently installed in the fuel tank as in the case of the fuel pump.
Here, FIG. 1 schematically illustrates an inside appearance of the fuel tank. Reference numeral 1 denotes an in-tank tube (reference numeral 1′ denotes an in-tank tube on a return side typically provided in the case of a diesel car, and the in-tank tube 1′ is equal to the in-tank tube 1), reference numeral 2 denotes the fuel tank, reference numeral 3 denotes the fuel, reference numeral 4 denotes a filter, reference numeral 5 denotes the fuel pump, reference numeral 6 denotes a jet pump, reference numeral 7 denotes a housing made of polyoxymethylene (POM), and reference numeral 8 denotes a spring. That is, the fuel 3 in the fuel tank 2 passes the filter 4 so as to be fed into the in-tank tube 1 by the fuel pump 5, and is then fed as it is to an external fuel circuit such as an engine. Then, the housing 7 including the in-tank tube 1 and the like is provided with the springs 8 for corresponding to the deformation of the fuel tank 2 due to thermal expansion. In addition, the in-tank tube 1 is typically of a bellows structure as illustrated in the figure for corresponding to the deformation of the fuel tank 2 due to expansion and the absorption of the vibration of the pump. It should be noted that the fuel 3 on the return side is returned into the housing 7 by the Venturi effect of the jet pump 6.
By the way, the outer peripheral surface of the hose as well as the inner peripheral surface of the hose are requested to have resistance against sour gasoline produced by the oxidation of the fuel 3 resulting from the manner in which the in-tank tube 1, which is provided in such state as described above, is used (sour gasoline resistance). In view of the foregoing, measures have been conventionally taken to meet such request by forming the entirety of the hose from a material excellent in, for example, sour gasoline resistance such as a polyamide 11 (PA11) or a polyamide 12 (PA12) (see, for example, Patent Literature 1).